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排序方式: 共有1324条查询结果,搜索用时 15 毫秒
121.
W. T. Lee S. X. Ding D. K. Sun C. I. Hsiao C. P. Chang L. Chang P. W. Kao 《Metallurgical and Materials Transactions A》2011,42(9):2909-2916
Ultrafine-grained (UFG) Mg-3Al-1Zn (AZ31) alloys with gain sizes ranging from 0.46 to 3.22 μm were prepared by equal channel angular pressing (ECAP) and annealing. The deformation structure of UFG AZ31 alloy resulting
from uniaxial compression was studied by optical and electron microscopy. The deformation was noted to proceed with the development
of shear bands (SBs), which has not been reported in an UFG hcp metal. Characterization of these SBs was performed, and comparison
with the SBs formed in UFG bcc and fcc metals was given. { 10[`1]2} \{ 10\bar{1}2\} tension twins inside SBs were found in all specimens compressed, irrespective of the grain size. Discussion on the limiting
grain size of twinning in the UFG AZ31 alloy is also given. 相似文献
122.
Stamford P. Bickford T. Hsiao H. Mattern W. 《IEEE engineering in medicine and biology magazine》1999,18(4):45-52
Telemedicine is evolving into an important tool in delivering services to emergency departments (EDs) in rural areas. However, we do not yet know what kinds of services can be effectively delivered or the degree to which these services might be useful. In this pilot study, a high-speed, high-quality video, 24-hour ATM (asynchronous transfer mode) network linked a rural ED to an ED of a major medical center. The objective was to measure the utilization of telemedical consulting services. Specifically, this one-year study examined the significance of telemedicine in changing diagnosis and treatment and the influence on patient transfers 相似文献
123.
A series of novel organosoluble and light‐colored fluorinated poly(ether imide)s (PEIs) ( IV ) having inherent viscosities of 0.43–0.59 dL/g were prepared from 4,4′‐[1,4‐phenylenbis(isopropylidene‐1,4‐phenyleneoxy)]diphthalic anhydride ( I ) and various trifluoromethyl‐substituted aromatic bis(ether amine)s by a standard two‐step process with thermal and chemical imidization of poly(amic acid) precursors. These PEIs showed excellent solubility in many organic solvents and could be solution‐cast into transparent and tough films. These films were essentially colorless, with an UV–visible absorption edge of 361–375 nm and a very low b* value (a yellowness index) of 15.3–17.0. They also showed good thermal stability with glass‐transition temperature of 191–248°C, 10% weight loss temperature in excess of 494°C, and char yields at 800°C in nitrogen more than 39%. The thermally cured PEI films showed good mechanical properties with tensile strengths of 83–96 MPa, elongations at break of 8–11%, and initial moduli of 1.7–2.0 GPa. They possessed lower dielectric constants of 3.25–3.72 (1 MHz). In comparison with the V series nonfluorinated PEIs, the IV series showed better solubility, lower color intensity, and lower dielectric constants. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 620–628, 2007 相似文献
124.
A novel anthraquinone‐containing bis(ether amine) monomer, 2,6‐bis(4‐aminophenoxy)anthraquinone, was synthesized from readily available reagents. A series of novel aromatic polyimides were prepared from the newly synthesized diamine monomer with various aromatic tetracarboxylic dianhydrides. The intermediate poly(amic acid)s had inherent viscosities of 0.67–1.12 dL g?1, and those derived from less stiff dianhydrides could be solution‐cast and thermally cyclodehydrated into flexible and tough polyimide films. The polyimides exhibited glass transition temperatures between 270 and 297 °C, and they were fairly stable up to a temperature of 500 °C in air or nitrogen. The electrochemical and electrochromic properties of one of the polyimides were investigated. The polymer could undergo two reversible steps of electrochemical reduction, with a color change from a colorless neutral state to pink and rose‐red reduced states. © 2012 Society of Chemical Industry 相似文献
125.
This study investigates the effects of using fuels with low heating values on the performance of an annular micro gas turbine
(MGT) experimentally and numerically. The MGT used in this study is MW-54, whose original fuel is liquid (Jet A1). Its fuel
supply system is re-designed to use biogas fuel with low heating value (LHV). The purpose is to reduce the size of a biogas
distributed power supply system and to enhance its popularization. This study assesses the practicability of using fuels with
LHVs by using various mixing ratios of methane (CH4) and carbon dioxide (CO2). Prior to experiments, the corresponding simulations, aided by the commercial code CFD-ACE+, were carried out to investigate
the cooling effect in a perforated combustion chamber and combustion behavior in an annular MGT when LHV gas was used. The
main purposes are to confirm that there are no hot spots occurring in the liners and the exhaust temperatures of combustor
are lower than 700°C when MGT is operated under different conditions. In experiments, fuel pressure and mass flow rate, turbine
rotational speed, generator power output, and temperature distribution were measured to analyze MGT performance. Experimental
results indicate that the presented MGT system operates successfully under each tested condition when the minimum heating
value of the simulated fuel is approximately 50% of pure methane. The power output is around 170 W at 85000 r/min as 90% CH4 with 10% CO2 is used and 70 W at 60000 r/min as 70% CH4 with 30% CO2 is used. When a critical limit of 60% CH4 is used, the power output is extremely low. Furthermore, the best theoretical Brayton cycle efficiency for such MGT is calculated
as 23% according to the experimental data while LHV fuel is used. Finally, the numerical results and experiment results reveal
that MGT performance can be improved further and the possible solutions for performance improvement are suggested for the
future studies. 相似文献
126.
Vaccinia virus has a wide host range and infects mammalian cells of many different species. This suggests that the cell surface receptors for vaccinia virus are ubiquitously expressed and highly conserved. Alternatively, different receptors are used for vaccinia virus infection of different cell types. Here we report that vaccinia virus binds to heparan sulfate, a glycosaminoglycan (GAG) side chain of cell surface proteoglycans, during virus infection. Soluble heparin specifically inhibits vaccinia virus binding to cells, whereas other GAGs such as condroitin sulfate or dermantan sulfate have no effect. Heparin also blocks infections by cowpox virus, rabbitpox virus, myxoma virus, and Shope fibroma virus, suggesting that cell surface heparan sulfate could be a general mediator of the entry of poxviruses. The biochemical nature of the heparin-blocking effect was investigated. Heparin analogs that have acetyl groups instead of sulfate groups also abolish the inhibitory effect, suggesting that the negative charges on GAGs are important for virus infection. Furthermore, BSC40 cells treated with sodium chlorate to produce undersulfated GAGs are more refractory to vaccinia virus infection. Taken together, the data support the notion that cell surface heparan sulfate is important for vaccinia virus infection. Using heparin-Sepharose beads, we showed that vaccinia virus virions bind to heparin in vitro. In addition, we demonstrated that the recombinant A27L gene product binds to the heparin beads in vitro. This recombinant protein was further shown to bind to cells, and such interaction could be specifically inhibited by soluble heparin. All the data together indicated that A27L protein could be an attachment protein that mediates vaccinia virus binding to cell surface heparan sulfate during viral infection. 相似文献
127.
The set of frequent closed itemsets uniquely determines the exact frequency of all itemsets, yet it can be orders of magnitude smaller than the set of all frequent itemsets. In this paper, we present CHARM, an efficient algorithm for mining all frequent closed itemsets. It enumerates closed sets using a dual itemset-tidset search tree, using an efficient hybrid search that skips many levels. It also uses a technique called diffsets to reduce the memory footprint of intermediate computations. Finally, it uses a fast hash-based approach to remove any "nonclosed" sets found during computation. We also present CHARM-L, an algorithm that outputs the closed itemset lattice, which is very useful for rule generation and visualization. An extensive experimental evaluation on a number of real and synthetic databases shows that CHARM is a state-of-the-art algorithm that outperforms previous methods. Further, CHARM-L explicitly generates the frequent closed itemset lattice. 相似文献
128.
Unbounded model checking fundamentally requires either image or preimage calculations. We introduce a hybrid method for making preimage calculations using ATPG and binary decision diagrams (BDDs). Experimental results show that the proposed method achieves a speedup of two to three orders of magnitude over pure ATPG methods. 相似文献
129.
Patel (1981) proposed a probabilistic approach to analyze the performance of synchronous multistage interconnection networks (MINs) based on a uniform reference model and the assumption of independent requests. Patel's model and analytical results have been widely adopted by numerous researchers as a basis to investigate various aspects of MINs. We study in detail the effects of the independence assumption on the accuracy of system performance and point out the factors which cause an inaccuracy. A new queueing model is then proposed and is shown to be very accurate. Since only six states are needed, independent of the size of MINs, this new model is very efficient computationally 相似文献
130.
Jack F. Smith Ming-Yuan Hsiao Thomas F. Lin Michael G. Willis 《Nuclear Engineering and Design》1991,125(2)
The phenomena of liquid metal flow under the influence of magnetic and electric fields are important in the development and design of nuclear and metallurgical plants, such as the blanket cooling systems of fusion or fast breeder reactors and electromagnetic stirring devices. In this study, a computer code that models recirculating flows in two dimensions using a k − ε turbulence model is expanded to include the magnetohydrodynamic (MHD) effects of applied electric and magnetic fields. This modified code is then used to examine the effect of MHD stirring on the heat transfer characteristics of a liquid metal cooling system. Using liquid sodium properties, various thermophysical properties are investigated. The results indicate that a significant increase in the rate of heat transfer is obtainable when the heat transfer system is operated in the presence of MHD stirring. 相似文献